Researches have recently been under way for improving the capacity of a flywheel apparatus for storing electrical energy. For this purpose, it is useful to employ a flywheel having a large momentum, and rotating at a high speed. As a result, large flywheels having a weight of several tens of tons to several hundred tons have come to be used. This increase in size of flywheels has, however, given rise to a lot of technical problems. One of them is concerned with a means for stopping the motion of a flywheel when power supply has been interrupted.
FIG. 1 shows by way of example a known flywheel apparatus for storing electrical energy. A motor dynamo 1 for energy conversion functions as a motor when energy is stored, and as a dynamo when energy is released. A flywheel 2 is rotated by the motor dynamo 1 for storing electrical energy by converting it to rotatory inertial energy. The flywheel 2 is connected to the rotor of the motor dynamo 1 by a coupling 3. The rotary shafts of the rotor and the flywheel 2 are rotatably supported by ball-and-roller bearings 4a, 4b and 4c. A thrust bearing device 5 supports the rotary part of the apparatus, including the flywheel 2, and comprises a fixed thrust bearing 5a. A magnetic bearing 6 includes a magnetic coil 7. The flywheel 2, the thrust bearing device 5 and the magnetic bearing 6 are accommodated in a casing 8 having an interior 9 in which a vacuum is maintained for minimizing the windage loss arising from the rotation of the flywheel 2. Seals 10 are provided for the ball-and-roller bearings 4b and 4c to maintain the vacuum in the casing interior 9. The thrust bearing device 5 further includes a thrust plate 11 attached to a lower flywheel shaft 12. The weight of the rotatory part of the apparatus is partially supported by the thrust bearing 5a.
The following is a description of the operation of the known apparatus as hereinabove described. When the apparatus is in normal operation, the majority of the weight of its rotatory part, usually at least about 90%, is supported by the magnetic bearing 6, so that the load on the bearings 4a to 4c may be reduced. The remaining weight of the rotatory part of the apparatus is supported by the thrust plate 11 on which the hydraulic fluid fed through the thrust bearing 5a in the direction of an arrow A exerts a slight hydraulic pressure. The hydraulic fluid present between the thrust bearing 5a and the thrust plate 11 also provides a damping effect on the vertical vibratory motion of the flywheel 2. As an evacuating device not shown maintains the vacuum in the interior 9 of the casing 8, the rotation of the flywheel 2 is hardly affected by any windage loss.
Under normal conditions, the apparatus continues stable operation very satisfactorily. Once the power supply fails, however, electricity ceases to be supplied to the magnetic bearing 6, and a pump provided for feeding a hydraulic fluid through the thrust bearing 5a in the direction of the arrow A, though not shown. The magnetic bearing 6 loses its attractive force, and the supply of the hydraulic fluid to the thrust bearing 5a is interrupted. As a result, the whole weight of the rotatory part of the apparatus bears on the thrust bearing device 5, and the bearings 4a to 4c. The rotatory part is very heavy. For example, the flywheel 2 usually has a weight of several tens of tons to several hundred tons. It is entirely difficult to support by the bearings 4a to 4c. If the weight is to be supported by the thrust bearing device 5, it is necessary to enlarge the thrust bearing 5a and the thrust plate 11 in outside diameter to increase their loading capacity to decrease the mean surface pressure acting thereon. A very large thrust bearing is required. It is difficult to cool the thrust bearing satisfactorily, since the operation of the feed pump stops, and the supply of the cooling fluid is interrupted. There is always a considerably long time before the operation of the apparatus stops completely. It is often difficult to maintain a sufficiently high fluid pressure and a sufficiently large fluid quantity, even if the fluid is supplied by gravity from a separate fluid reservoir.